Axial Piston Machine Having an Inclined-Axis Construction

ABSTRACT

An axial piston unit ( 1 ) having bent-axis construction with several guided piston elements ( 3 ) longitudinally movable in one rotatable cylinder device ( 2 ) and with an area ( 4 ) operatively connected with the piston elements ( 3 ) and guided with torque. The torque-guided area ( 4 ) is constructed to be rotatable around a swivel axis ( 10 ), and a displacement of the axial piston unit ( 1 ) varies depending on the rotary movement of the torque-guided area ( 4 ).

FIELD OF THE INVENTION

The invention relates to an axial piston unit having bent-axis construction with several guided piston elements are longitudinally movable in one rotatable cylinder device and with an area operatively connected with the piston elements and guided with torque.

BACKGROUND

In practice, axial piston units are used for the drive of the widest variety of hydraulically operable devices and the conversion of torque. This arises, among other things, from the high power density of axial piston units, and the ability to continuously adjust the displacement.

Axial piston units are provided, for example, as hydraulic drives for hydraulically operated machines, such as excavator arms and buckets, loading equipment of wheel loaders, extension handlers, bulldozers, load lifting devices of dump trucks, and the like. Moreover, integrating axial piston units into travel drives of such machines is also known, whereas the axial piston units represent parts of hydrostatic transmissions of single wheel drives or split power continuously variable transmissions.

Thereby, adjustable axial piston units are preferably used with swashplate or bent-axis construction, whereby axial piston units constructed as swashplate pumps (due to their design) are typically realized with an adjustable angle of a maximum of +/−21 degrees. Due to the limited adjustment angle area (due to their design), swashplate units are characterized by a low power density, and are thereby constructed in a size that is relatively large, in order to be able to make available a corresponding amount of power or convert this to the desired extent.

Furthermore, swashplate units also exhibit a low degree of efficiency, as piston elements slide along a swashplate by means of sliding shoes, and the piston elements are thereby subjected to transverse forces. The transverse forces acting on the piston elements result from the frictional forces arising in operation in the connection area between the piston elements and each of the cylinders assigned to the piston elements, which adversely affect the degree of efficiency.

In addition, leakage currents, which adversely affect the volumetric degree of efficiency of a swashplate unit, arise in the area of the columns between the piston elements and the respectively assigned cylinders.

Compared to swashplate units, axial piston units having bent-axis construction are able to be operated with higher degrees of efficiency, whereas, with conventionally constructed bent-axis units, a maximum adjustment angle amounts to approximately 25 degrees. However, such bent-axis units are typically not able to be swiveled through.

If bent-axis units operate as pumps, they are typically employed in open circuits. In order to reflect a changing direction of oil flow in the area of a bent-axis unit, the direction of rotation of a bent-axis unit must change. If axial piston pumps having bent-axis construction are constructed without a torque-guided area and a synchronous hinge connected to a cylinder device, transverse forces must be transferred, with certain disadvantages, from the piston elements between the cylinder device and the torque-guided area, in order to be able to support the frictional forces between the cylinder device and a valve plate. The piston ends of the piston elements are typically captured in calottes, and at that point, transfer the piston force into an axial force and a circumferential force.

Although the degrees of efficiency of bent-axis units are higher than the degrees of efficiency of swashplate units described above, based on the constructive conditions briefly described below, the power density of bent-axis units generally always lies below the desired range.

Bent-axis units, in particular bent-axis pumps, that are known are typically constructed with a fixed drive shaft axis and a rotatably constructed cylinder device. An oil guide between a standing housing and the rotatably constructed cylinder device is typically effected by means of a sliding tray.

In order to ensure that the oil guide has a flow of leakage volume that is as small as possible, a corresponding sealing must be provided. However, the sealing is limited to a maximum swivel angle of the cylinder device, upon which a maximum displacement, and thus a power density of a bent-axis unit, is dependent, such that the power density is low.

DE 10 2007 033 008 A1 discloses an axial piston unit having bent-axis construction, the total swivel angle range of which amounts to 90 degrees, whereas a cylinder device is rotatably constructed from a zero position, in which a displacement of the axial piston unit is equal to zero, in each case by +/−45 degrees. The cylinder device is mounted in a rotatable yoke housing. In an elaborate manner, the oil feeding the cylinder device and flowing from the cylinder device is, in the area of a yoke bearing, taken from a hydraulic system formed on the side of the housing, or fed into this. In doing so, the oil forwarded or sucked in by the piston elements in the cylinder device must be guided between the cylinder device or each piston area confined by the cylinder device and the piston elements and a yoke bearing through relatively long oil channels. This causes undesirably high pressure losses, and thus degrades the degree of efficiency.

In addition, in the area of the interface between the rotating yoke and a standing bearing support, i.e. in the area of the yoke bearing unit, a seal constructed for high operating pressures must be provided, which allows for a rotary movement of the yoke housing and the cylinder device and/or the cylinder drum against a torque-guided area and/or a drive plate of the axial piston unit.

Such bent-axis units indeed exhibit better degrees of efficiency than those with bent-axis machines constructed with a swivel angle of approximately 25 degrees, but the production costs are higher than those of the bent-axis machines with lower degrees of efficiency.

SUMMARY OF THE INVENTION

Therefore, an object of this invention is the task of providing an economically producible axial piston unit having bent-axis construction, which can be operated with a high degree of efficiency, and is characterized by a high power density. Additional objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In accordance with the invention, the tasks are solved with an axial piston unit with the characteristics of the appended claims.

The axial piston unit having bent-axis construction under the invention is constructed with several guided piston elements longitudinally movable in one rotatable cylinder device and with an area operatively connected with the piston elements and guided with torque.

In accordance with the invention, the torque-guided area is constructed to be rotatable around a swivel axis, and a displacement of the axial piston unit varies depending on the rotary movement of the torque-guided area. In this manner, sealing measures that increase the oil guides and production costs and impair the degree of efficiency of the axial piston unit are not provided for the axial piston unit under the invention. This arises from the fact that the oil flowing in and flowing out between the cylinder device and a fixed housing is interchangeable without the interconnection of long oil channels that produce large pressure losses, and the components constructed in a rotating manner around the fixed housing, in the area of which elaborate and costly sealing measures are typically provided, are not to be exchanged.

In addition, a swivel angle range of the axial piston unit under the invention is not limited by the unnecessarily elaborate sealing in the lesser extent, by which the axial piston unit under the invention is achievable with a power density that is higher than that of the known axial piston unit.

With a structurally simple embodiment that saves installation space and costs of the axial piston unit under the invention, the torque-guided area is a bevel, which can be brought into engagement with an additional bevel.

An embodiment of the axial piston unit under the invention that is likewise structurally simple and saves costs is characterized in that the torque-guided area is rotatably mounted around a bearing device absorbing axial and radial forces in a cage rotating around the swivel axis, in the area of which preferably a device generating the rotary movement can initiate a turning force.

With an additional embodiment of the axial piston unit under the invention that saves installation space, the swivel axis of the torque-guided area is arranged perpendicularly to a rotation axis of the cylinder device, and/or a rotation axis of the torque-guided area upon a displacement of the axial piston unit is equal to zero in alignment with the rotation axis of the cylinder device.

If the cylinder device in a housing is rotatably mounted around a bearing device absorbing axial and radial forces, the axial piston unit under the invention is achievable with a forced lubrication that is favorable for the degree of efficiency, through which only limited areas are provided with lubricating and cooling fluid. Thus, compared to the known axial piston unit, for which rotating components are fully arranged in an oil bath, the axial piston unit under the invention is to be operated in a structurally simple manner with a higher degree of efficiency.

With an additional embodiment of the axial piston unit operable with low steering and control effort, hydraulic channels on the side of the housing are able to be brought into operative connection with the piston areas confined by the piston elements and the cylinder device, depending on the rotary movement of the cylinder device.

If the torque-guided area is connected to the piston elements through piston slippers, and the piston elements are rotatably mounted in piston slippers, the axial piston unit under the invention is achievable with a swivel angle range allowing for a high power density.

If the torque-guided area and the cylinder device are operatively connected with one another in an articulated manner for speed synchronization through a wave-like element, the axial piston unit's piston elements in operation under the invention are essentially free of transverse forces, by which a high sealing effect in the area between the piston elements and the cylinder device is ensured with minimal effort.

If the cylinder device with a side turned away from the torque-guided area is attached to a valve plate fixed on the side of the housing, in the area of which each of the hydraulic channels flows into the areas that are preferably kidney-shaped, the axial piston unit under the invention is operable with a high degree of efficiency. That is because the cylinder device is rotatable around a thin oil film between the valve plate and the cylinder device, which is adjusted in operation of the axial piston unit, with low friction forces toward the valve plate.

Both the characteristics specified in the appended claims and the characteristics specified in the subsequent embodiments of the axial piston unit under the invention are, by themselves alone or in any combination with one another, suitable for providing additional embodiments under the invention. In terms of the additional embodiments under the invention, the particular combinations of characteristics do not represent a limitation; rather, they are essentially solely of an exemplary nature.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional benefits and advantageous embodiments of the axial piston unit under the invention arise from the appended claims and the embodiments described below, with reference to the drawing in terms of principle.

The following is shown:

FIG. 1 is a highly schematized representation of an embodiment of an axial piston unit having bent-axis construction under the invention in an initial operating condition; and

FIG. 2 is a representation corresponding to FIG. 1 of the axial piston unit in a second rotated operating condition of a torque-guided area.

DETAILED DESCRIPTION

Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

FIG. 1 shows a functional diagram of an embodiment of an adjustable axial piston unit 1 having a bent-axis construction. The axial piston unit 1 is constructed with several guided piston elements 3 longitudinally movable in one rotatable cylinder device 2 and with an area 4 operatively connected with the piston elements 3 and guided with torque. The piston elements 3 are sealed in the cylinder device 2 with suitable seals. In this embodiment, the axial piston unit 1 is formed as an axial piston pump having bent-axis construction, which is to be operated in a closed circuit. The cylinder device 2 is mounted in a housing 6, and rotatable around a rotation axis 5. The cylinder device 2 is rotatably mounted in the housing 6 around a bearing device 7 absorbing axial and radial forces. The axial forces of the cylinder device 2 are transferred to the housing 6. In this embodiment, the bearing device 7 is arranged radially between the piston elements 3 and the piston areas 8 confined by the cylinder device 2 in a favorable manner.

In this embodiment, the torque-guided area 4 is constructed as a bevel, which combs with an additional bevel 9, and is rotatable around a swivel axis 10 from the zero position presented in FIG. 1 to an initial swivel position shown in FIG. 2, which the axial piston unit 1 presents from a view in FIG. 1 more specifically described by the arrow II.

In the zero position of the crown wheel 4, an upstroke of the piston elements 3 in the cylinder device 2 and a displacement of the axial piston unit 1 is essentially equal to zero. A swivel angle between the rotation axis 5 of the cylinder device 2 and a rotation axis 11 of the torque-guided area 4 corresponds to that in the operating condition of the axial piston unit 1 presented in FIG. 2, essentially by around +45 degrees.

Moreover, the torque-guided area 4 is rotatable around the swivel axis 10 from the zero position presented in FIG. 1 to a second swivel position not shown in the drawing, by a swivel angle of −45 degrees.

Furthermore, the torque-guided area or the bevel 4, as the case may be, is rotatably mounted around a bearing device 12 absorbing axial and radial forces in a cage 13 rotating around the swivel axis 10, whereas, in this embodiment, the bearing device 12 includes a tapered roller bearing 14 and a cylindrical roller bearing 15.

In the zero position of the torque-guided area 4 and the cage 13 more specifically presented in FIG. 1, the rotation axis 5 of the cylinder device 2 and the rotation axis 11 of the torque-guided area 4 are in alignment or run in the same direction, as the case may be. For the rotating crown wheel 4 and the connected piston slippers 16, in the area of which the piston elements 3 are connected and rotatably mounted with the crown wheel 4, the cylinder device 2 is picked up through a wave-like element 17 or a synchronous hinge, as the case may be, through which the torque-guided area 4 and the cylinder device 2 are operatively connected with one another in an articulated manner for speed synchronization.

The wave-like element 17 or the synchronous hinge, as the case may be, which is intended for speed synchronization between the crown wheel 4 with the piston slippers 16 and the cylinder device 2, assists in supporting the friction forces arising in the area between the valve plate 18 fixed on the side of the housing and the cylinder device 2, and in moving the piston elements 3 into the cylinder device 2, essentially free of transverse forces.

This means that, through the wave-like element 17, the friction force taking effect between the cylinder device 2 and the valve plate 18 fixed on the side of the housing in the operation of the axial piston unit 1 is overcome. The cylinder device 2 with a side 19 opposite the torque-guided area 4 is attached to the valve plate 18 fixed on the side of the housing, in the area of which the hydraulic channels 20 on the side of the housing flow into the kidney-shaped areas 21.

The valve plate 18 is operatively connected with the housing 6 in a torque-proof manner.

In this embodiment, the valve plate 18 is provided as a sliding and sealing surface, whereas the flow of oil is effected between the housing 6 and the cylinder device 2 through the two areas 21 on the side of the valve plate, which are constructed in a kidney-shaped manner at least in certain areas, and the hydraulic channels 20. In the housing 6 constructed in this embodiment, the hydraulic channels 26 and 27 are optimally achievable in terms of a lower loss of pressure. Each of the hydraulic channels 20 on the sides of the valve plates 18 are, depending on the rotary movement of the cylinder device 2, alternately in operative connection with the piston areas 8 confined by the piston elements 3 and the cylinder device 2, in order to provide, for example, a hydraulically operated excavator arm in the desired size.

If, based on the zero position presented in FIG. 1, in the direction of the first maximum swivel position shown in FIG. 2, the crown wheel rotates around the swivel axis 10, a hub of the piston elements 3 in the cylinder device 2 increases up to a maximum hub value, which is equivalent to a maximum displacement of the axial piston unit 1. In the swiveled position of the cage 13 and the crown wheel 4 shown in FIG. 2, the rotation axis 5 of the cylinder device 2 and the rotation axis 11 of the torque-guided area 4 or the crown wheel, as the case may be, comprises an angle of 45 degrees.

For the rotating crown wheel 4 and the piston slippers 16 connected to it, the cylinder drum 2 is picked up through the wave-like element 17, and piston elements 3 are realized through the rotary movement of their maximum hub.

The swivel axis 10 of the crown wheel 4 and the cage 13 stands perpendicular to the rotation axis 5 of the cylinder device 2. In the embodiment under FIG. 1, the swivel axis 10 of the crown wheel 4 at the same time corresponds to a rotation axis of the additional crown wheel 9 and/or a shaft 22 that is thereby connected in a torque-proof manner to the crown weel 9. The shaft 22 is connected by a spur gear 23 to a mechanical transmission that is not more specifically shown, and that is, in the present case, rotatably mounted in a main housing 24 around a bearing device 25 absorbing axial and radial forces.

This means that, in the pump operation of the axial piston unit 1 through the shaft 22, mechanical power or torque is carried onto crown wheel 4, and mechanical power is extracted in a motor operation of the axial piston unit through the shaft 22.

Given that the cage 13 is constructed to be rotatable around the swivel axis 10, and that the rotating axis of the shaft 22, with which the additional crown wheel 9 is connected in a torque-proof manner, corresponds to the swivel axis 10, the drive of the crown wheel 4 through the additional crown wheel 9 is feasible without impairing the power transmission through the teeth of the crown wheel 4 and the additional crown wheel 9, even during the swiveling of the cage 13.

Depending on the respective application, there is also the option of providing, instead of the spur gear 23, another suitable shaft connection, such as a flange connection or the like, in order to introduce a torque applied to the crown wheel 4 into the mechanical transmission or transfer it from the mechanical transmission to the crown wheel 4.

The circumferential force in the gear meshing of the two bevels 4 and 9 must be supported through the adjusting device of the cage 13. Apart from this circumferential force, the adjusting device must also support the piston forces that are not 100% balanced.

Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims. 

1. (canceled) 2-10. (canceled)
 11. A bent-axis axial piston unit, comprising: a plurality piston elements; a rotatable cylinder device, the piston elements longitudinally movable within respective piston areas of the rotatable cylinder device; a driven torque-guided area member operatively connected with the piston elements; the torque-guided area member driven in a rotating path around a swivel axis; and wherein displacement of the axial piston unit is a function of rotary movement of the torque-guided area member in the rotating path.
 12. The bent-axis axial piston unit as in claim 11, wherein the torque-guided area member is a bevel, the bevel engageable with an additional drive bevel for driving the torque-guided area member in the rotating path around the swivel axis.
 13. The bent-axis axial piston unit as in claim 11, wherein the torque-guided area member is rotatably mounted with a bearing device that absorbs axial and radial forces the bearing device disposed within a cage that rotates around the swivel axis.
 14. The bent-axis axial piston unit as in claim 1, wherein the swivel axis is perpendicular to a rotational axis of the cylinder device.
 15. The bent-axis axial piston unit as in claim 14, wherein in a zero rotational position where a rotational axis of the torque-guided area member is in alignment with a rotational axis of the cylinder device, displacement of the piston unit is essentially zero.
 16. The bent-axis axial piston unit as in claim 11, wherein the cylinder device is rotatably mounted in a housing with a bearing that absorbs axial and radial forces.
 17. The bent-axis axial piston unit as in claim 11, further comprising a valve plate in communication with a side of the cylinder device opposite from the torque-guided area member, the valve plate having hydraulic channels that are brought into sequential fluid communication with the piston areas as a function of rotary movement of the cylinder device relative to the valve plate.
 18. The bent-axis axial piston unit as in claim 11, wherein each piston element is connected to the torque-guided area member with a piston slipper, the piston elements rotatably mounted in the respective piston slippers.
 19. The bent-axis axial piston unit as in claim 11, wherein the torque-guided area member is connected to the cylinder device in an articulated manner for speed synchronization through a wave-like member.
 20. The bent-axis axial piston unit as in claim 19, wherein the cylinder device is rotatable within a housing, and further comprising a valve plate connected to a side of the housing opposite from the torque-guided area member, the valve plate having oppositely disposed kidney-shaped hydraulic channels that are brought into sequential fluid communication with the piston areas as a function of rotary movement of the cylinder device relative to the valve plate. 